1. Field of the Invention
This invention relates to an improvement in a conventional rotary head device for a magnetic recording/reproducing apparatus.
2. Description of the Prior Art
The size of rotary head type magnetic recording/reproducing apparatus (VTRs) has recently been reduced to a significant extent. As a result, portable VTRs are becoming more popular. To meet this tendency, efforts have been made to reduce the size and thickness of rotary head devices for such VTRs. Such efforts, however, have approached a structurally allowable limit. A typical example of conventional rotary head devices is shown in FIG. 1 of the accompanying drawings. In the conventional device, a rotating shaft 2 is disposed at the center of a fixed lower drum 1. The rotating shaft 2 is rotatably attached to the fixed lower drum 1 by bearings 3 and 4. A rotary upper drum 5 which is opposed to the fixed lower drum 1 is attached to a support member 6 by a mounting screw 7. The support member 6 is secured to the rotating shaft 2 above the bearing 3. The rotary upper drum 5 is thus arranged to be rotatable relative to the fixed lower drum 1. At least one head base plate 10 which is provided with a magnetic head 9 is mounted on the rotary upper drum 5 by mounting screws 11. The peripheral faces of the rotary upper drum 5 and the fixed lower drum 1 serve as magnetic tape travelling faces. A winding 12 on the rotating side of a rotary transformer is mounted on the support member 6 while a winding 13 on the stationary side thereof is mounted on the fixed lower drum 1 opposite to the winding 12. The winding 12 on the rotating side is connected to the magnetic head 9. Input and output signals to and from the magnetic head 9 are thus arranged to pass through the magnetic coupling of the rotary transformer.
Another support member 14 is mounted on a part of the rotating shaft 2 below the bearing 4. A rotary yoke 16 of a motor 15 is mounted to the support member 14 by means of a mounting screw 17. The rotary yoke 16 has a rotary magnet 18 secured thereto. Opposite to the rotary magnet 18, there are provided a stator 19 and a stator coil 20 which is secured to the fixed lower drum 1.
In the conventional rotary head device shown in FIG. 1, the rotary upper drum 5 is mounted on the rotating shaft 2 while the rotating shaft 2 is supported by the bearings 3 and 4. Such being the arrangement, if the spacing between these bearings 3 and 4 is arranged to be short, the rotation locus of the magnetic head 9 would be affected and the head 9 would be prevented from making a precise rotation by a tilt of the rotating shaft 2 due to deviation of the bearings 3 and 4 from their prescribed relative positions. Because of this problem, it has been extremely difficult to reduce the thickness of a rotary head device in the axial direction thereof. Further, in accordance with the conventional arrangement, the rotation precision of the rotary upper drum 5 consists of the sum of the degrees of precision of bearings 3 and 4, the rotating shaft 2, the support member 6 and the rotary upper drum 5. Accordingly, a great expenditure has been necessary in order to secure the individual precision of these parts as well as the engagement precision between them. Another problem of the conventional device resides in that the pre-load setting for the bearings 3 and 4 is effected by fixing the support member 6 to the rotating shaft 2. However, since the fixed lower drum 1 and the rotating shaft 2 differ from each other in thermal expansion coefficient, temperature variations tend to cause the pre-load on the bearings 3 and 4 to disappear.